I'm sorry for the late reply but there have been the Christmas vacation in the meantime and I wanted to perform some tests as you suggested.
I've tried to calibrate my monitor once again but I had some problems (I'm opening a new topic about it) so I keep using the older monitor profile.
I've created my monitor profile with i1ProfilerD2Lidition and the I've analyzed it with ColorThinkPro.
Where do you find the RGB primaries values?
For Shaper/Matrix profiles in the Red, Green, Blue Colorant Tags of the profile
I don't really get what you mean when you say: "Scanner RGB values outside the gamut of the IT8 target were extrapolated."
Scanner or camera device RGB values which were outside the Lab values of the IT8 target or portion of the RGB gamut area of the device that were beyond or outside the Lab gamut area of the target. The Lab gamut then need to be expanded to reach the edge boundary of the RGB gamut by extrapolation.
The un-modified camera profile I've originally created as a gamut volume of 2.609.160.
The modified camera profile I was referring to before was highly desaturated for having a kind of sepia-effect. That's probably the reason for the small gamut volume?
The IT8 gamut is small compare to your camera profile. It encompasses maybe only about 20% of your camera gamut while the 80% were extrapolated and likely very inaccurate and furthermore your camera profile was also modified. My suggestion: 1) Find ways to reduce the RGB gamut to fit the Lab gamut better and reprofile your camera. 2) Avoid photographing scenes that are high saturated or beyond the IT8 color gamut or saturation. 3) Convert directly to monitor space. Converting to prophoto or adobergb is needless especially from your small gamut edited camera profile if you aren't doing any color editing in photoshop.
thing that I don't understand is why, if I apply a small gamut volume profile, the image posterizes. Shouldn't it be the contrary? For example when you apply ProPhoto to a picture that is 8bit.
Please read above
I'm playing around with the image you gave me but, so far, applying the various profiles, it doesn't posterize.
Its probably scene dependent. Use a test target made specifically for camera and not for scanner. Test targets for camera profile your camera to different real life scenes while scanner IT8 targets profile your camera only to printed photographs.
But I'm wondering now...
When you create a custom ICC Profil for you camera (without making some strange tweaks as I am doing) what is the standard way to convert it to Adobe 1998 or ProPhoto, in order to leave you colors as they are (obviously to certain degrees...)?
either Relative or Absolute colorimetry.
Thank you very much!